The Alu family represents the most ubiquitous interspersed repeated DNA sequence in the primate genome. There are about 500,000 of these 300 bp elements and they appear to amplify themselves throughout the genome via an RNA mediated mechanism termed retroposition. Because these sequences have a modest preference for integrating in gene-rich regions of the genome, we would expect that their interspersion would result in significant damage to the genome. We do know of several cases where these insertions have led to disease and it is certain that many more such events have occurred in the past, but not been passed on because of their lethality. Thus, it is important to understand the method and rate of amplification of these sequences, as well as its regulation. Recent evolutionary studies suggest that the vast majority of Alu family members are pseudogene copies of a limited set of "master" genes. The data are consistent with the possibility that there has only been one master gene responsible for the majority of Alu amplification and evolution. It is our goal to molecularly clone an Alu "master" gene and determine whether it has bene the primary source of all Alu amplifications. The isolation of this master gene will allow us to determine whether this gene is under evolutionary selection, and therefore may have a function. It will also lead to studies which will define the expression pattern and regulation of this gene and potentially to a laboratory system in which the Alu retroposition process can be characterized. It is also possible that it will provide us with the opportunity to determine whether there is a significant level of Alu amplification in somatic cells, perhaps leading to tumors in some cases. Previous efforts to clone an Alu master gene have been thwarted by the extremely high copy number of Alu sequences that must be sorted through to find the master. We had previously defined a subfamily of 500 sequences that are the most recently inserted and came from a distinct master gene. More recently, an Alu family member has been found that inserted in the NF1 gene of a patient, causing neurofibromatosis. This insertion occurred during the last generation and, although it had all the markings of our recent subfamily, it also had two new sequence changes. We can now use those two changes as molecular handles to isolate the master gene which made that most recent insertion. This will then allow us to determine the qualities that define a master gene.